MMP14 enhances tumour growth and invasion in hepatocellular carcinoma

Abstract

Matrix metalloproteinase (MMP) family consists of more than 25 zinc-dependent endopeptidases. While most of them are secretory zymogens, MMP14 is a transmembrane protein. It is involved in tissue remodeling and embryonic development. It also contributes to metastasis (Nat Rev Cancer, 2:161-174, 2002) and angiogenesis by increasing vascular endothelial growth factor (VEGF) (FASEB, 16:555-564, 2002). MMP14 directly participates in tumour invasion through activation of MMP2, which degrades components of the ECM. In our microarray study (Mol Biol Cell, 13:1929-39, 2002), it was identified to be up-regulated specifically in hepatocellular carcinoma (HCC) with histological evidence of venous invasion, a microscopic feature that demonstrated presence of tumor cells in the vascular space lined by endothelial cells. Venous invasion associated with metastasis and recurrence, but the underlying mechanism is still unclear. In the current study, we observed that both the active 60kD and catalytically inactive 45kD forms in the tumour revealed an increased level compared to its adjacent non-tumour by western blot. The 45kD form was the result of autocatalytic mechanism of the active MMP14, which would be internalized and recycled for rapid relocation of fresh enzymes at the leading invasive front (J Cell Sci 116:3905-3916, 2003). Therefore, its presence in HCC tumor but not in non-tumor indirectly reflects the existence of active MMP14 on cell surface and the ability to activate pro-MMP2 (Cancer Sci 94:569-574, 2003). By immunohistochemistry study on clinical specimens, MMP14 demonstrated heterogeneous expression in the tumor tissues while hepatocytes surrounding the veins in the non-tumour tissues showed positive signal. The difference in MMP14 localization and species between tumour and non-tumour suggests this protein may act as determinant in different steps of cell invasion process. To further understand how MMP14 functionally affect the process of tumour invasion, we have cloned the MMP14 cDNA. The gene was overexpressed in a HCC cell line, Hep3B, and the performance was analyzed in various steps of cell invasion. Compared with the control transfectants, overexpression of MMP14 promoted cell growth, increased cell invasion, adhesion efficiency and migration ability of the HCC cells in vitro. The effect of MMP14 overexpression was also examined in vivo by implantation of transfectants into the liver of nude mice. MMP14-transfected xenografts showed enhanced growth rate and increased frequency of intrahepatic metastasis, compared with the control transfectants. All these data support the role of MMP14 in HCC invasion. Invasion and metastasis are the principal causes of death in HCC patients. They also have a profound impact on prognosis and disease recurrence after tumour resection. The current study provided evidence that MMP14 is involved in tumour invasion and MMP14 could be essential as a novel targets for HCC treatment.